The present invention relates generally to fluid valves, for example valves which may be used to deliver hot and cold water to a common spout.
Compression valves are often used to control fluid flow, for example water flow, from a fluid source to a fluid outlet. In such valves used in water fixtures, a stem is moved axially to open and shut the valve to allow passage of water from a water source to a water outlet. A flange is often provided at the end of the stem to prevent passage of water back through the valve when the valve is open.
Such compression valves may be advantageous when the water outlet includes a squeeze nozzle commonly fed by a pair of valves. Typically, the separate valves respectively control the flow of water from a hot water source and a cold water source to the common squeeze nozzle. In this arrangement, the valves are normally left open to some degree so that water under pressure is always delivered to the nozzle, and water flow is activated by the squeeze nozzle. Since the valves share a common water outlet, if water pressure in one of the water lines is greater than the pressure in the other, water from the higher pressure line may force its way through the other valve into the lower pressure line.
The flange on a compression valve stem, which permits passage of water out through the valve but not back through, generally prevents the back flow problem. Specifically, if water from the higher pressure line is forced back through the other open valve, the reverse water flow moves the flange to block the valve entrance and prevents water flow back into the lower pressure line.
Shear valves may also be used in such water flow systems. In a typical shear valve, abutting flat circular plates are disposed in a cylindrical housing and rotate with respect to each other. The plates have openings which, depending on the rotational position of the plates, may align to allow water passage from the valve's entrance to its exit. Rotation of the plates in a closing direction, however, blocks water passage. A stem is attached to one of the plates so that rotation of the stem rotates the plate with respect to the other plate, which is rotationally fixed with respect to the housing.
Unlike the compression valves described above, shear valves generally do not have a mechanism to prevent reverse water flow through the valve when the valve is open. Accordingly, a check valve may be installed in the water line upstream from the shear valve. Alternatively, if a shear valve is to be retrofit into a fixture originally equipped with a compression valve, the water line may be cut to permit check valve installation.